Witnesses are being asked to come forward after a man was robbed in Hertfordshire on Thursday 1 November.
Four men approached the 20-year-old on London Road in Knebworth at about 1.15am. Two of them were wearing Halloween masks - one of a skeleton and the other a clown. The two other men had covered their faces with scarves.
The victim was punched in the face and suffered a cut lip and a swollen eye. He also handed over some money and his mobile phone.